1. Field of the Invention
The invention concerns circuits for reducing the power consumed by fluorescent lighting fixtures and by high-intensity, low-voltage incandescent lighting fixtures By "low-voltage" is meant less than 50 volts. When used with fluorescent lighting fixtures, the power consumed is reduced either by allowing a lamp of a fixture to be removed or by reducing the power consumed by the lamp or lamps of the fixture.
2. Description of Related Art
A high-intensity, low-voltage incandescent lamp which operates from AC household current requires a current-limiting, voltage-reducing circuit, invariably a wound-wire transformer that often draws current when the lamp is turned off. The transformers are expensive, bulky, heavy, and have energy losses associated with the hysteresis and eddy currents in the laminated steel cores of their transformers.
Fluorescent lamps also require current-limiting circuits that are usually called a "ballast", invariably including a wound-wire transformer. Most overhead fluorescent lighting fixtures accept at least one pair of lamps. Currently many of these fixtures are being modified by replacing one of the lamps with a dummy lamp, thus producing nearly 50%. savings in power while reducing the light output 50%. However, the reduction in actual illumination can be much less than 50% by installing a metallized reflective film above the remaining lamp.
Several types of dummy lamps are shown in U.S. Pat. No. 4,107,581. (Abernethy), each having an external appearance similar to that of a conventional fluorescent lamp except that there is no need for air-tight seals between the tubular body and the end caps. In the dummy lamp of FIG. 1, a pin of each end cap is connected to a pin of the other end cap by a wire that is designed to simulate the steady state of a conventional fluorescent lamp. In the dummy lamp of FIG. 2 the two pins of each end cap are interconnected by a resistor "to simulate the resistive effect of the cathode heaters in a conventional rapid start fluorescent lamp" (col. 5, 1s. 2-14). The linear centers of those resistors are in turn interconnected by a wire to simulate the relatively low electrical resistance between the two cathode heaters of a conventional fluorescent lamp.
In the dummy lamp of FIG. 2B which the Abernethy patent says is less preferred than those of FIGS. 1, 2 and 2A, "a capacitor 19a which is preferably a relatively large electrolytic capacitor, is coupled in the line 19" between the two resistors 17" and 18". . . . Several of the drawbacks to using the insert 11" including the capacitor 19a include the added expense of the capacitor, the undesirable heat generated in and emanating from the capacitor, a reduced light output level of any remaining fluorescent lamp coupled in the ballast circuit, possible detrimental effects on the remaining components of the ballast circuit, and a possible reduction in life of any such remaining fluorescent lamps" (col. 6, 1s. 10-33).
The dummy lamps of FIGS. 2b and 4 of U.S. Pat. No. 3,956,665 (Westphal) appear to be similar to that of FIG. 2B of the Abernethy patent except that a capacitor is connected directly between one pin at each of its end caps. Although I do not find in the Westphal patent any description of those capacitors except that they should be from 4 to 8 mfd in a replacement for a 40 w lamp in 120 v fixture, they would be inoperative if they were (according to Abernethy's suggestion) electrolytic capacitors. As is pointed out in Grob: "Basic Electronics," McGraw Hill, 5th Ed. (1984) at page 400:
"If the electrolytic (capacitor) is connected in opposite polarity, the reversed electrolysis forms gas in the capacitor. It becomes hot and may explode. This is a possibility only with electrolytic capacitors."
Dummy lamps like those of FIGS. 2b and 4 of Westphal are currently being marketed as DSI "Phantom" Tube Model PTF 40 by Developmental Sciences, Inc. to replace 40w fluorescent lamps in 120v fixtures. Each of these dummy lamps employs a rolled-film capacitor of about 4 mfd that is about 5 cm long and 3 cm in diameter and is marked with the Westphal patent number.
In the dummy lamp of FIG. 5 of U.S. Pat. No. 4,255,692 (Burgess) "is a conventional capacitor 32 and which is connected to at least one of the terminals 28 and 30 on each of the end caps, respectively, by means of an electrical conductor 34" (para. bridging cols. 7 and 8). Other figures of the Burgess drawing show similarly connected capacitors, but I fail to find in the Burgess patent any description of those capacitors.
U.S. Pat. No. 4,348,614 (Burgess) points out that because of their considerable length, dummy lamps are expensive, both to manufacture and to ship. He obviates this problem by a shortened lamp substitute such as that shown in FIG. 5 which includes a capacitor connected between one pin of an end cap and ground. In FIG. 13, Burgess connects his lamp substitute to socket of a 2-lamp fixture. Except that Burgess says his FIG. 5 uses "a conventional capacitor" (col. 8, line 31), I fail to find any description of the capacitor.
Lamp substitutes similar to FIG. 5 of Burgess '614 have been marketed by Remtec Systems as "No-Watt" Model SP-3-30A and Model SP-350, both containing rolled-film capacitors. The former is marked with U.S. Pats. No. 4,317,069 and 4,475,064.
Instead of a lamp substitute, U.S. Pat. No. 3,954,316 (Luchetta) provides an attachment for a 2-lamp fluorescent fixture that reduces both the power and the light output while illuminating both lamps. Luchetta's attachment 46 of FIG. 1 includes a small isolation transformer 39 and a capacitor 45 connected between the primary and secondary windings 41 and 43 respectively. In the example which employs a nonpolar capacitor of 20 mfd for a 2-lamp, 40 w, 120 v fixture, "the illumination intensity was reduced by 12% with a reduction in input power of 15.6%" (col. 7, 1s. 53-54).